PHP MySQL：如何确定数据库中是否已存在值

Question

I have a form button that I need to do two different things, based on user input and whether that input already exists in my database. If the input DOES NOT exist, then the button will create a new record. If it DOES exist, then the existing record will be updated.

Here's my PDO query as it stands now:

/* First, we need to discover whether the Proposal No. entered already exists in the
database. If it doesn't, then a new record will be created. If                                                                            
it does, then an existing record will be updated. */
$pNoExists = $con->prepare("SELECT ProposalNo FROM ptfp1"); 
$pNoExists->execute();
$row = $pNoExists->fetch(PDO::FETCH_ASSOC);

When I run $row = $pNoExists->fetch(PDO::FETCH_ASSOC); through a while loop, all of the values for the field are present. Now I just need some guidance on how to use that in my button setup. This is what I want to do:

if($_POST['ButtonPush'] && input doesn't exist) {
  Create new record;
}
else {
  Update existing record;
}

Simple, right? But it's eluding me.

Answer 1

Given what you have, I would do:

if($_POST['ButtonPush'] && array_search($all_values, $input_value)) {
    Create new
}
else {
    Update
}

However, like the comment above, you may want to simply add a where clause to your "SELECT" statement so you are not grabbing the entire database table contents every time. And, one could even convert the SELECT in to a SELECT COUNT to bring down the amount of data being requested.